An air filter designed to remove particulate matter from an airstream generally is a device comprising fibrous materials. These fibrous materials may remove solid particulates such as dust, pollen, mold, and bacteria from the airstream. Air filters are used in applications where air quality is important, notably in building ventilation systems and with engines.
Air filters may be used in automobiles, trucks, tractors, locomotives, and other vehicles that use internal combustion engines. Air filters may be used with gasoline engines, diesel engines, or other engines that utilize fossil fuels or other combustible substances. Air filters may be used with engines in which combustion is intermittent, such as four-stroke and two-stroke piston engines, as well as other types of engines that take in air continuously so that a combustible substance may be burned. For example, air filters may be used with some gas turbines. Filters may also be used with air compressors or in other devices that take in air.
Filters may be made from pleated paper, foam, cotton, spun fiberglass, or other known filter materials. Generally, the air filters used with internal combustion engines and compressors tend to be comprised of either paper, foam, or cotton filters. Some filters use an oil bath. Air filters for internal combustion engines prevent abrasive particulate matter from entering the cylinders of the engine, where it would cause mechanical wear and oil contamination. In many fuel injected engines, a flat panel pleated paper filter element may be used. This filter is usually placed inside a plastic box connected to the throttle body with ductwork. Vehicles that use carburetors or throttle body fuel injection typically use a cylindrical air filter positioned above the carburetor or throttle body.